The noncovalent conjugations of human serum albumin (HSA) with MS/AK and the effect on anti-oxidant capacity as well as anti-glycation activity of Monascus yellow pigments

Deciphering the inhibitory mechanisms of betanin and phyllocactin from Hylocereus polyrhizus peel on protein glycation, with insights into their application in bread

Protein glycation closely intertwines with the pathogenesis of various diseases, sparking a growing interest in exploring natural antiglycation agents. Herein, high-purity betacyanins (betanin and phyllocactin) derived from Hylocereus polyrhizus peel were studied for their antiglycation potential using an in vitro bovine serum albumin (BSA)-glucose model. Notably, betacyanins outperformed aminoguanidine, a recognized antiglycation agent, in inhibiting glycation product formation across different stages, especially advanced glycation end-products (AGEs). Interestingly, phyllocactin displayed stronger antiglycation activity than betanin. Subsequent mechanistic studies employing molecular docking analysis and fluorescence quenching assay unveiled that betacyanins interact with BSA endothermically and spontaneously, with hydrophobic forces playing a dominant role. Remarkably, phyllocactin demonstrated higher binding affinity and stability to BSA than betanin. Furthermore, the incorporation of betacyanins into bread dose-dependently suppressed AGEs formation during baking and shows promise for inhibiting in vivo glycation process post-consumption. Overall, this study highlights the substantial potential of betacyanins as natural antiglycation agents.

Revealing the Hypoglycemic Effect of Red Yeast Rice: Perspectives from the Inhibition of α-Glucosidase and the Anti-Glycation Capability by Ankaflavin and Monascin

Red yeast rice dietary supplements have been proven to ameliorate hyperglycemia, but the mechanism was unclear. In this work, ankaflavin (AK) and monascin (MS), as typical pigments derived from red yeast rice, were found to exert noteworthy inhibitory ability against α-glucosidase, with an IC50 of 126.5 ± 2.5 and 302.6 ± 2.5 μM, respectively, compared with acarbose (IC50 = 341.3 ± 13.6 μM). They also exhibited mixed-type inhibition of α-glucosidase in vitro and caused fluorescence quenching through the static-quenching process. Molecular-docking studies indicated that AK and MS bind to amino acid residues outside the catalytic center, which induces structural changes in the enzyme, thus influencing its catalytic activity. The anti-glycation ability of Monascus-fermented products was evaluated, and they exhibited a high inhibition rate of 87.1% in fluorescent advanced glycation end-product formation at a concentration of 0.2 mg mL-1, while aminoguanidine showed a rate of 75.7% at the same concentration. These results will be significant in broadening the application scope of Monascus pigments, especially AK and MS, in treating type 2 diabetes.

Effects of two food colorants on catalase and trypsin: Binding evidences from experimental and computational analysis

Recently, growing concern has been paid to the toxicity of additives in food. The present study investigated the interaction of two commonly used food colorants, quinoline yellow (QY) and sunset yellow (SY), with catalase and trypsin under physiological conditions by fluorescence, isothermal titration calorimetry (ITC), ultraviolet-vis absorption, synchronous fluorescence techniques as well as molecular docking. Based on the fluorescence spectra and ITC data, both QY and SY could significantly quench the intrinsic fluorescence of catalase or trypsin spontaneously to form a moderate complex driven by different forces. Additionally, the thermodynamics results demonstrated QY bind more tightly to both catalase and trypsin than SY, suggesting QY poses more of a threat to two enzymes than SY. Furthermore, the binding of two colorants could not only lead to the conformational and microenvironmental alterations of both catalase and trypsin, but also inhibit the activity of two enzymes. This study provides an important reference for understanding the biological transportation of synthetic food colorants in vivo, and enhancing their risk assessment on food safety.

Binding of ankaflavin with bovine serum albumin (BSA) in the presence of carrageenan and protective effects of Monascus yellow pigments against oxidative damage to BSA after forming a complex with carrageenan

Ankaflavin (AK) is a typical yellow pigment extracted from Monascus-fermented rice with several biological effects; however, its solubility is poor. Thus, research studies of the delivery systems of AK, especially those constructed from protein-polysaccharide complexes, have attracted considerable attention. However, the interactions that exist in the system have rarely been investigated. This work focused on the interactions between AK and bovine serum albumin (BSA) as well as the influence of carrageenan (Car) on the binding of AK to BSA. Results revealed that the quenching of BSA by AK involved the static quenching mechanism. The formed BSA-AK complexes were mainly maintained by hydrophobic forces and AK was located within the hydrophobic cavity of BSA. Compared to free AK or AK only complexed with BSA, a higher absorption intensity of AK was observed for the formed BSA-AK-Car complexes, indicating changes in the microenvironment of AK. This was confirmed by the increase in the α-helix content of BSA after the formation of BSA-AK-Car complexes. Hydrogen bond, van der Waals, and electrostatic interactions were verified to be the primary forces preserving the BSA-AK-Car complexes. Moreover, the antioxidant potential of Monascus-fermented products rich in AK (denoted as Mps), namely BSA-Mps and BSA-Mps-Car was evaluated. The antioxidant activity of Mps was negatively impacted by BSA, while the addition of Car could enhance the antioxidant capacity of BSA-Mps-Car complexes. Meanwhile, Mps showed a protective effect against free radical-induced oxidation damage to BSA, and Car could further improve this effect.

Molecular Insight into the Binding of Astilbin with Human Serum Albumin and Its Effect on Antioxidant Characteristics of Astilbin

Astilbin is a dihydroflavonol glycoside identified in many natural plants and functional food with promising biological activities which is used as an antioxidant in the pharmaceutical and food fields. This work investigated the interaction between astilbin and human serum albumin (HSA) and their effects on the antioxidant activity of astilbin by multi-spectroscopic and molecular modeling studies. The experimental results show that astilbin quenches the fluorescence emission of HSA through a static quenching mechanism. Astilbin and HSA prefer to bind at the Site Ⅰ position, which is mainly maintained by electrostatic force, hydrophobic and hydrogen bonding interactions. Multi-spectroscopic and MD results indicate that the secondary structure of HSA could be changed because of the interaction of astilbin with HSA. DPPH radical scavenging assay shows that the presence of HSA reduces the antioxidant capacity of astilbin. The explication of astilbin–HSA binding mechanism will provide insights into clinical use and resource development of astilbin in food and pharmaceutical industries.

Multispectroscopic and synergistic antioxidant study on the combined binding of caffeic acid and (-)-epicatechin gallate to lysozyme

The binding of caffeic acid (CA) and/or (-)-epicatechin gallate (ECG) to lysozyme was investigated by multispectroscopic methods and molecular docking. The effects of the single and combined binding on the structure, activity and stability of lysozyme and the synergistic antioxidant activity of CA and ECG were also studied. Fluorescence quenching spectra, time-resolved fluorescence spectra, and UV-vis absorption difference spectra all ascertained the static quenching mechanism of lysozyme by CA/ECG. Thermodynamic parameters indicated that CA and ECG competitively bound to lysozyme, and CA had a stronger binding affinity, which was consistent with the results of molecular docking. Hydrogen bonding, van der Waals' force and electrostatic interaction were the main driving forces for the binding process. Synchronous fluorescence spectra displayed that the interaction of CA/ECG exposed the tryptophan residues of lysozyme to a more hydrophilic environment. Circular dichroism spectroscopy, Fourier transform infrared spectroscopy and dynamic light scattering indicated that the binding of CA and/or ECG to lysozyme resulted in the change of the secondary structure and increased the particle size of lysozyme. The binding of CA and/or ECG to lysozyme inhibited the enzyme activity and enhanced the thermal stability of lysozyme. The combined application of CA and ECG showed antioxidant synergy which was influenced by the encapsulation of lysozyme and cellular uptake. In summary, this work provides theoretical guidance for lysozyme as a carrier for the combined application of CA and ECG.

Isolation and characterization of the anthocyanins derived from red radishes (Raphanus sativus L.) and the protective ability of β-lactoglobulin against heat-induced oxidation

This study employed the "two-step dialysis" method and AB-8 or D101 macroporous resin chromatography to isolate the anthocyanins in red radishes (ARR). The red radish juice was dialyzed twice at 3000 and 500 Da, respectively. UHPLC-QqQ-MS/MS revealed 24 types of ARRs, of which pelargonidin (Pg)-3-diglucoside-5-(malonyl)glucoside (P3D5MG), Pg-3-diglucoside-5-glucoside (P3D5G), Pg-3-(feruloyl)diglucoside-5-(malonyl)glucoside (P3FD5MG), Pg, and malvidin (Mv) represented the main compounds. The total anthocyanin content in the ARR prepared via the "two-step dialysis" method was 29.69% and 18.44% higher than that obtained using AB-8 and D101 macroporous resins, respectively. The ARRs inhibited heat-induced β-lactoglobulin (β-Lg) oxidation. The amino acid residue microenvironment and secondary β-Lg structure were modified via ARR binding. The energy involved in P3D5MG and β-Lg binding was -392 kJ/mol, which was significantly lower than that during the binding process of P3D5M, P3FD5MG, Pg, and Mv to β-Lg (-338 to -168 kJ/mol). These results indicated that "two-step dialysis" was a promising method for deriving natural pigment with strong antioxidant activity from red radishes. PRACTICAL APPLICATION: As a natural food colorant, anthocyanins have attracted increasing attention in the food industry in recent years. This study used "two-step dialysis" to effectively separate ARRs. Moreover, the anthocyanins in ARR can bind to β-Lg to protect against heating-induced oxidation. Therefore, ARRs may not only act as a food pigment but also as antioxidants.

Structurally diverse Monascus pigments with hypolipidemic and hepatoprotective activities from highland barley Monascus

Highland barley Monascus has historically been used in solid state fermentation and traditional fermented foods in Tibet. It is possessed of the characteristics of medicine and food. Three new 8,13-unsaturated benzocyclodiketone-conjugated Monascus pigments (1-3), three new benzofuran Monascus pigments (4-6), three new butylated malonyl Monascus pigments (7-9), and eleven known Monascus pigment derivatives (10-20) were isolated from highland barley Monascus for the first time. Their structures were determined by analyzing NMR, MS, UV, and IR spectral data and compared with relevant references. Among them, compounds 2, 4, 6 showed important inhibition of pancreatic lipase activity, and decreased significantly FFA-induced lipid accumulation in HepG2 liver cells. Additionally, compounds 1, 10, 14, 16, 18 exhibited certain hepatoprotective activities against the damage in acetaminophen-induced HepG2 cells. The plausible biogenetic pathway and preliminary structure activity relationship of the selected compounds were scientifically summarized and discussed in this work.